Used oil drained from internal combustion engines may contribute to soil, surface water, and groundwater contamination if not properly managed. Traditionally vehicle motor oil has been changed on a routine basis, usually either at mileage or time intervals. These intervals were generally conservative to avoid any possibility of engine damage, and led to the need to responsibly dispose of billions of gallons of used oil per year.
A more recent development has been the development of algorithms or sensors to estimate or directly measure the state of the oil and signal its need for replacement only when its lubricating capability fell below acceptable levels. This has generally led to longer oil change intervals than the previous routine approach and has reduced, but not minimized or eliminated, the volume of used oil requiring disposal.
Oils are generally complex mixtures of chemical compounds characterized by a base stock and a combination of additives, collectively described as an additive package, selected to improve specific performance attributes. Traditionally the base stock was a petroleum hydrocarbon derived from crude oil. Increasingly, however, synthetic base stocks such as polyalphaolefin (PAO) or synthetic esters and related synthetics such as alkylated napthalenes and alkylated benzenes are used. In general, both the base stock and the additive package are selected to convey desired oil attributes at a level commensurate with the oil's intended application.
The need to change oil is driven by the need to remove contaminants and to replenish the additive package which is progressively consumed or ‘used up’ with use. Most of the base stock itself does not “break down”, although minor quantities which lubricate the cylinder walls and migrate past the piston rings may be combusted in the combustion chamber. Hence “used” oil may be viewed as primarily unused oil with contaminants coupled with an absence of, or a reduced quantity of, additives.
Thus the volume of used oil requiring disposal could be further reduced if the particle contamination could be managed and if the additive package could be replenished. With these adjustments, and possibly some minor addition of unused oil, used oil could be regenerated to offer the lubricating and engine protection capability substantially identical to that of unused oil.